This patent is an improvement of my patent titled xe2x80x9cAir Vehicle Having Scissors Wingsxe2x80x9d with U.S. Pat. No. 6,601,795B1 and Date of Patent Aug. 5, 2003.
Not Applicable.
Not Applicable.
1. Field of Invention
The invention relates to air vehicles such as manned and unmanned air vehicles and, in particular, to air vehicles that can fly both in helicopter mode and airplane mode to achieve vertical and/or short take-off and landing (V/STOL) and improve their flying efficiency at a wide range of speed and flying conditions.
2. Description of Prior Art
Various attempts have been made to combine helicopter""s excellent capability of vertical and/or short take-off and landing and fixed-wing aircraft""s ability of flying at a wide range of speed.
U.S. Pat. No. 5,454,530 xe2x80x9cCanard Rotor/Wingxe2x80x9d issued to J. W. Rutherford et al invents an aircraft utilizing a jet-propelled rotor/wing, preferably having two blades, to achieve V/STOL when it is in helicopter mode. During the conversion from the helicopter mode to airplane mode, the aircraft utilizes its canards and horizontal tail to generate most of the lift to offload the rotating rotor/wing. Afterwards, the rotating speed of the rotor/wing is slowed down and eventually stopped so that the aircraft is in airplane mode with the two blades of the rotor/wing become the left and right wing of the aircraft. When flying in airplane mode, the rotor/wing can operate like an oblique wing to maximize flight efficiency at different speeds.
A disadvantage of this invention is that different requirements to the canards and horizontal tail at different flying conditions force these aerodynamic surfaces to compromise their key parameters. The canards and horizontal tail should generate almost all the lift for the aircraft during the conversion between helicopter mode and airplane mode, but they are mainly used as control surfaces at other flying stages. As the canards and horizontal tail should be large enough to generate almost all the lift for the aircraft but they are mainly used as control surfaces at airplane mode, they make the aircraft inefficient at airplane mode.
U.S. Pat. No. 3,327,969 xe2x80x9cConvertible Aircraftxe2x80x9d issued to R. E. Head is an invention also utilizes a jet-propelled rotor/wing. During V/STOL, the rotor/wing rotates like a helicopter and generates lift with three stub blades installed on a big center body of the rotor/wing. During the conversion between helicopter mode and airplane mode, the big center body generates lift while the rotor/wing stops or begins to rotate. At airplane mode, the center body and two of the three stub blades generate lift for the aircraft.
This invention has a disadvantage of low flying efficiency. The relatively small and low aspect ratio stub blades are not efficient in generating lift at helicopter mode. In addition, the center body, which has a very small aspect ratio, has to generate almost all the lift during the conversion between helicopter mode and airplane mode. As the conversion should be made at a low speed, this low aspect ratio center body has to have large area to generate enough lift because its lift-to-drag ratio (L/D) is low. Furthermore, at airplane mode, one of the three stub blades is located with its long axis generally parallel with the longitudinal axis of fuselage, generating little lift.
Patent JP 404317891A xe2x80x9cAircraft For Vertical Take-Off And Landingxe2x80x9d issued to H. Hatano is an invention utilizing two sets of rotor/wings that can convert between rotors and fixed wings. The two sets of rotor/wings are either mounted above the fuselage of an aircraft in tandem with one rotor/wing in front of another, or co-axially installed above the fuselage with one rotor/wing above another. During take-off, landing, and low speed flying, the rotor/wings rotate in opposite directions to make the aircraft fly like a helicopter. At high speed, both of the rotor/wings stop rotating to become fixed wings and the yaw angles of both fixed wings can be changed to fit different speeds.
One disadvantage of this invention is its complexity. When both of the rotor/wings are installed co-axially above the fuselage, the hub of the rotor/wings should contain mechanisms to control the collective pitch and cyclical pitch of the two counter-rotating rotor/wings at helicopter mode and the sweep angles of both of the rotor/wings at airplane mode. Having so many control mechanisms, the hub is not only complex but also difficult to have small size thus generates considerable drag during high-speed flights.
Another disadvantage is poor controllability and stability. During the conversion between helicopter mode and airplane mode, both of the rotor/wings have to keep generating lift to support the aircraft while they are being stopped or started to rotate, making the aircraft difficult to have good controllability and stability during the conversion.
X-wing configuration, as shown in U.S. Pat. No. 4,711,415 xe2x80x9cX-Wing Helicopter-Scout Attack Configurationxe2x80x9d issued to J. A. Binden, consists of a rotor/wing that can rotate as a rotor at helicopter mode and a fixed xe2x80x9cXxe2x80x9d shaped wing at airplane mode. The fixed sweep angles of the blades of the X-wing are affected by the requirements of helicopter mode, making them usually be a 45-degree sweep-forward angle for two blades and a 45-degree sweepback angle for the other two blades. These fixed sweep angles make a X-wing aircraft difficult to achieve efficient flying at a wide range of speed at airplane mode.
U.S. Pat. No. 2,879,013 xe2x80x9cConvertible Aircraftxe2x80x9d issued to G. P. Herrick is an invention utilizing a straight rotor/wing and a straight fixed wing. At helicopter mode, the straight rotor/wing rotates like a two-blade rotor of a helicopter. At airplane mode, the rotor/wing is stopped and together with the fixed wing, forming a configuration similar to a biplane. This invention cannot make an aircraft fly at high speed because the two straight wings can generate huge drag at high speed flying.
The fundamental object and advantage of my invention is to build an air vehicle that can efficiently and effectively achieve V/STOL and fly at a wide range of speed up to supersonic speed. Specifically, the objects and advantages of an air vehicle based on my invention are:
1. Have V/STOL capability;
2. Can easily convert between helicopter mode and airplane mode;
3. Can efficiently and effectively fly at a wide range of speed up to supersonic speed;
4. Can fly at transonic and low supersonic speed without generating sonic boom.
A rotor/scissors wing configuration has been invented to achieve the above-mentioned objects and advantages. The invention has a fuselage, a rotor/scissors wing, and a scissors wing. The rotor/scissors wing is installed above the fuselage and the scissors wing is rotatably mounted on the fuselage. The following paragraphs explain how can the invention realize the above-mentioned four objects and advantages.
First, an air vehicle based on the invention can have V/STOL capability. At helicopter mode, the rotor/scissors wing rotates in a way similar to rotors of helicopters. There are two ways to drive the rotation of the rotor/wing. The first way is to direct the exhaust gas from at least one turbofan or turbojet engine to the jet nozzles located on the rotor/scissors wing to propel it to rotate. Another way is to transmit the shaft power generated by at least one turboshaft/turbofan convertible engine via a transmission system to drive the rotor/scissors wing to rotate. Tested on engines like the turboshaft/turbofan convertible engine based on a modified General Electric TF34 engine, turboshaft/turbofan convertible engines can work at both turbofan mode to provide thrust and turboshaft mode to provide shaft power.
When using the exhaust gas from turbofan or turbojet engines, the rotating rotor/scissors wing generates little, if any, torque moments on the air vehicle thus no anti-torque device like tail rotor is required. However, in order to achieve yaw control of the air vehicle at V/STOL, hovering, and very low speed flying, a small fan, or rotor, or thruster is required for air vehicles using turbofan or turbojet engines. When using turboshaft/turbofan convertible engines to drive the rotor/scissors wing to rotate, an anti-torque device like a fan, a rotor, or a thruster is required. This anti-torque device is also used to gain the yaw control of the air vehicle during V/STOL, hovering, and low speed flying. The pitch and roll control of the air vehicle under both of the engine arrangements can be achieved by adjusting the cyclic pitch and collective pitch of the rotating rotor/scissors wing similar as helicopters. These engine arrangements and control methods can ensure the air vehicle to achieve V/STOL, hovering, and low speed flying like a helicopter.
Second, an air vehicle based on the invention can easily convert between helicopter mode and airplane mode. After take-off, the rotating rotor/scissors wing accelerates the air vehicle in helicopter mode. With speed increasing, the scissors wing generates more and more lift, offloading the rotating rotor/scissors wing. In the mean time, more and more engine power is used to directly generate thrust to propel the aircraft instead of rotating the rotor/scissors wing. Finally, all of the engine power is used to directly propel the air vehicle and the rotor/scissors wing is slowed down and locked at a position where its long axis is generally perpendicular to the longitudinal axis of the fuselage, virtually forming a biplane together with the scissors wing. Similarly but in a reverse order, the air vehicle can convert from airplane mode to helicopter mode. The stopping and starting of rotation of the rotor/scissors wing do not change or disturb the center of lift of the air vehicle because it generates none or little lift, making the air vehicle easy to control and have good stability during the conversion.
Third, an air vehicle based on the invention can efficiently and effectively fly at a wide range of speeds up to supersonic speed. At airplane mode, the air vehicle is of scissors wings configuration with the rotor/scissors wing acting as another scissors wing. By adjusting the yawing angle of both the rotor/scissors wing and scissors wing, the air vehicle can maximize its flying efficiency at virtually any speed within its flight envelope. When yawed to a big angle from perpendicular to fuselage, the cross-sectional areas of both the rotor/scissors wing and scissors wing are generally evenly distributed along the longitudinal axis of the fuselage, making the air vehicle very easy to conform to the xe2x80x9carea rulexe2x80x9d for transonic and supersonic flying. This feature makes the air vehicle have low transonic and supersonic drag thus have high efficiency in transonic and supersonic flying as well as subsonic flying.
Different from the canard rotor/wing configuration of U.S. Pat. No. 5,454,530, the scissors wing of this invention is used to generate lift during the entire course of flying except hovering, vertical take-off and landing, and very low speed flying. This makes the air vehicle more efficient than canard rotor/wing configuration whose canards and horizontal tail generate lift only in the conversion between helicopter mode and airplane mode and are used mainly as control surfaces at airplane mode.
Forth, an air vehicle based on the invention can fly at transonic and low supersonic speed without generating sonic boom. When yawed at a big angle from perpendicular to fuselage, the supersonic drag characteristics of an air vehicle with scissors wings is similar to that of an air vehicle with oblique wing because both have similar cross-sectional area distribution along the longitudinal axis of fuselage, and both are composed of generally straight and continuous wing or wings yawing at an angle. According to U.S. Pat. No. 3,971,535 xe2x80x9cOblique-Wing Supersonic Aircraftxe2x80x9d issued to R. T. Jones, oblique wing configuration can make an air vehicle fly up to Mach 1.3 without generating sonic boom. As the scissors wings configuration has similar supersonic drag characteristics as oblique wing configuration, air vehicle with rotor/scissors wing can also fly at transonic and low supersonic speeds without generating sonic boom. This feature makes an air vehicle with rotor/scissors wing able to fly over population centers at a supersonic speed without disturbing people on the ground.